A method and an arrangement for controlling the rpm of a drive unit is disclosed with respect to the example of an rpm control in U.S. Pat. No. 4,441,471. There, a control of the idle rpm is carried out at least in the idle operating state of the drive unit in dependence upon a pregiven rpm desired value and a measured rpm actual value by actuating a positioning element controlling the rpm of the drive unit. The rpm desired value is dependent upon operating variables. The start phase of the drive unit is also considered in addition to the normal control range. If the rpm is still below a pregiven minimum rpm, then the control element, which controls the rpm, is driven with a pregiven fixed drive signal to ensure adequate start air. When the minimum rpm is exceeded, a control of the rpm in the idle state takes place with the aid of a controller. The controller includes a proportional component, an integral component and a differential component.
In some applications, this known solution displays an unsatisfactory performance during the start phase. Because of the specific characteristics at start, the rpm exhibits a clear overshoot in this phase above the steady-state rpm provided in the subsequent operation. The known controller reacts to the occurring rpm deviation starting when the minimum rpm is exceeded so that especially its integral component operates in an unfavorable operating range during the rpm overshoot. The transient state of the rpm to the steady-state desired rpm is correspondingly uncomfortable. Comparable effects are exhibited not only by rpm controllers but also by controllers which control a variable, which is related to the rpm, such as the torque, the supplied air, the power, the output rpm, et cetera.
It is an object of the invention to provide measures in combination with a method and an arrangement for the control of rpm of a drive unit wherein the performance of the drive unit is improved in the start phase.
The method of the invention is for controlling the rpm of a drive unit and includes the steps of: providing a controller having at least first and second components; and, with the start of the drive unit, forming a control signal with the controller by first activating the first component so that the control signal is based on the first component and thereafter activating the second component so that the control signal is based on both the first and second components.
The separate activation of components of the controller, which carries out the rpm control, optimizes the start phase of the drive unit. Under the term xe2x80x9cstart phasexe2x80x9d, the actual start including post-start is understood starting with the actuation of the starter or the switching on of the supply voltage (ignition on) up to the transient state to the steady-state rpm. With the relatively early activation of the proportional component and/or the differential component, the rpm overshoot is effectively countered by the controller without a disadvantageous control performance occurring in the subsequent transient or settling operation. This is so because the integral component of the control, as a rule, is activated later than the dynamic controller components.
It is especially advantageous that a constant position of the throttle flap is adjusted during the actual start phase and the activation of the controller to minimize the rpm overshoot takes place via a separate activation of the controller components. In this way, a simplification of the application of the start operation and especially the formation of the overshoot is achieved because the controller characteristics and/or the changing ambient conditions are of no consequence in the context of the actual start phase.
It is especially advantageous that a pregiven time is provided which ensures an activation also of the integral component of the controller in the case of an unfavorable drag torque.
Furthermore, a further time condition is provided in an advantageous manner via which a forced activation of all components of the controller takes place, for example, when there is a defective start or a poor start.